The influence of dirt track hardness on equine limb acceleration and impact attenuation

Track hardness is a modifiable factor that may influence musculoskeletal loading and injury risk in equine athletes. The purpose of this study was to evaluate the effects of track hardness on segmental accelerations and impact attenuation in the equine forelimb at racing speeds. We hypothesized that harder surfaces would result in greater peak segmental accelerations and reduced attenuation. Twelve Thoroughbred chuckwagon outriding horses, instrumented with tri-axial accelerometers and a global positioning system (GPS) unit, galloped on the Calgary Stampede dirt racetrack with different track preparations. Track hardness was varied through harrowing depth and moisture content and measured using a surface impact tester. Track conditions were grouped into soft (22.3–26.3 g), medium (38.1–44.3 g), and hard (61.2 g). Peak resultant hoof impact accelerations were 19% greater on the medium tracks when compared to the softer tracks. Peak axial and resultant cannon impact accelerations were 16–54% greater on the medium and hard tracks when compared to the soft tracks. Attenuation from hoof to cannon was not affected within the range of dirt track hardness tested. These results demonstrate that forelimb segmental accelerations are affected by track preparation manipulations within a single dirt track at galloping speeds. This may have implications for track preparation and injury risk management.